César Schirmer dos Santos is an Associate Professor at the Department of Philosophy of the Federal University of Santa Maria. He works on the metaphysics of memory.
A post by César Schirmer dos Santos
Are memory and imagination two manifestations of the same capacity? Some recent work on the psychology and neuroscience of remembering gave philosophers a new occasion for revisiting this classical question. Based on evidence from the study of amnesiac patients, Tulving (1985) hypothesized that the abilities to episodically remember one’s own past and imagine future personal episodes are two sides of a coin. In line with this hypothesis, neuroimaging studies revealed that your brain operates similarly when you remember the madeleine you ate yesterday at your mother’s house and when you imagine yourself eating a madeleine at your house tomorrow morning (Okuda et al. 2003; Addis, Wong, and Schacter 2007). Still, a widely discussed question is how these two mental time travel abilities relate to each other. Are they fundamentally the same?
The empirical evidence is inconclusive. On the one hand, the neurocognitive system of episodic simulation flexibly uses the acquired “vocabulary” of objects and properties found in the past to construct re-experiences and pre-experiences (Suddendorf and Corballis 1997; Addis, Wong, and Schacter 2007). Thus, there is a continuity between episodic remembering and episodic anticipation (Suddendorf, Addis, and Corballis 2009). On the other hand, imagining the future is more effortful to the mechanism than remembering the past (Okuda et al. 2003, 1369). Thus, there is a discontinuity between the two varieties of episodic simulation (Schacter et al. 2012). But it is unclear whether the difference is of nature or degree.
Bearing this in mind, at least at the moment, the observation of the brain is not sufficient for answering our question—an opportunity for empirically informed armchair philosophers. Below, I propose simplified schemes that summarize some essential points of the philosophical debate about the (dis)continuity between memory and imagination.
Before moving on, I clarify that I will not speak about remembering in general, but only of episodic remembering as the re-experience of fragments of an event from the personal past. I will talk about imagination only as of the episodic anticipation of pieces of an event that may come to pass at some point in the future life (Perrin 2016, 39). I follow Mahr’s (2020) practice of calling “episodic simulation” rather than “episodic memory” the shared system that generates episodic remembering and anticipation. The reason is that if the system makes you able to mental time travel to the past and to the future, it is not clear whether “‘episodic memory’ is the most appropriate descriptor for this system” (Addis, Wong, and Schacter 2007, 1375). By merely adopting Mahr’s terminology, I’m not taking sides. I’m just bringing out an inconclusive―at least for the sake of the nature/degree debate―empirical element accepted by all debaters.
Claims about mental content and mental processes are the main reasons for adopting a continuist view about mnemicity—i.e., the criterion for distinguishing memory from imagination (Michaelian and Sutton 2017). A straightforwardly continuist thesis is ContC.
ContC. Episodic remembering and episodic anticipation are continuous because they have the same kind of mental content.
As an explanatory thesis, ContC has the virtues of simplicity (Ockham’s razor) and durability. First, what is presented through these perhaps different varieties of mental states is something―an event―that can be similarly detached from the immediate external perceptual experience. Second, ContC is the traditional thesis that imagination is the ersatz for the past that exists no more: “it is the objects of imagination that are remembered in their own right” (Aristotle ±350BCE/2004, 450 a 23). Thus, the content of memory/imagination is “the phantasm remaining after the object is removed or past” (Hobbes 1640/1839, part 4, chap. 25, §7, 396).
There are two objections to ContC. The first objection concerns the relationship between reality and mental content. For a direct realist, the event you experienced in the past (instead of an image of this event) constitutes part of the content of your episodic remembering experience. Reid (1785/1857) and Aranyosi (2020) support this point of view. But the events you will possibly experience in the future do not constitute your episodic anticipations. Thus, memory and imagination are discontinuous.
The problem with this objection is that direct realism about memory is obscure. Relations require the existence of relata. But it is not clear whether the past exists. Even in the case of the existence of the past, it is not clear how you could get in touch with it in the present.
The second objection concerns the explanatory power of ContC. The continuist faces a dilemma. On the one hand, if ContC is the thesis that memory content includes images, it is trivial. On the other hand, ContC needs to be improved to explain the relationship between time and content. The trouble is that either the content conveys temporal information, or the temporal information is carried on by another means. But for a content vehicle to represent time, this vehicle has to contain verbs (Aristotle ±350BCE/1996, 1, 16 b 5–10). Still, in contrast to sentences, images have no such power (Russell 1921/2005, 212).
Focusing on this dilemma’s second horn, the solution is to put the temporal information outside the content. Compare a regular photo to an animated GIF. Both are composed of images, but the GIF changes. Maybe episodic simulation is “dynamic” (De Brigard and Gessell 2016, 170) like GIFs. Thus, it informs about time without including time in the content.
In sum, a continuist that accepts a somewhat modified version of ContC explains the similarity between memory and imagination by the shared kind of GIF-like content.
Another continuist thesis is ProcC.
ProcC. There is a continuity between episodic remembering and episodic anticipation because they are outputs of the same mechanism.
Modulo the focus on memory/imagination instead of remembering/anticipating, Hobbes’s epistemology is the classical rendering of ProcC as a theory about the shared mechanism. A sensation is the alteration of a sensory organ by the pressure of an external body. When the pressure ends, imagination (memory) begins. I.e., imagination/memory is “nothing else but sense decaying, or weakened, by the absence of the object” (Hobbes 1640/1839, part 4, chap. 25, §7, 396). This decline process explains why, in memory, “many accidents and places and parts of things, which were formerly perceived by sense, are by length of time decayed and lost” (Hobbes 1640/1839, part 4, chap. 25, §8, 398–399).
Michaelian’s (2016a; 2016b) theory of episodic remembering as mental time travel, or simulationism, is a contemporary defense of ProcC. Simply put, Michaelian claims that a person remembers an event from her past if, frequently and reliably, her episodic simulation mechanism generates content that corresponds to what happened.
Against ProcC, discontinuists point to evidence that the mechanisms for memory and imagination are different. There are two sorts of objections. First, some discontinuists point to differences internal to the episodic simulation system. Memory and imagination of autobiographical events involve the representation of the self in time. But the process for the simulation of the self in time is different in each case. Episodic remembering requires only the detection of yourself as the one that experienced the event in the past. In contrast, episodic anticipation involves the assignment of yourself as the one that would face the simulated event in the future (Perrin 2016, 56). Since it is plausible that there are different mechanisms for self-detection and self-assignment, probably ProcC is false.
The second discontinuist objection to ProcC involves a hypothesis about neural differences external to episodic simulation. According to Werning’s (2020) trace minimalism, ProcC is compatible with the fact that another mechanism cooperates in the production of episodic memories but not episodic anticipations.
The internal and external objections to ProcC explain the discontinuities between remembering and imagining observed in neuroimaging studies. In this sense, they point to differences in nature, rather than merely differences in degree, between remembering and imagining.
In my view, these objections to ProcC are the main challenge to continuism. Even if we accept that remembering and imagining have the same kind of content, we must accept that these are similar products of different processes. That is a good reason to claim that episodic remembering is not continuous to episodic anticipation.
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Acknowledgments. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001, process 88887.468340/2019-00. Thanks to Matheus Diesel Werberich and Eduardo Vicentini de Medeiros for reading and commenting a previous version of this text.
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